This invention relates to apparatus for carrying out false twisting of a yarn by clamping the yarn between opposing faces of two rotary discs.
Recently, there is a tendency of using DTY (Draw Textured Yarn) technique for performing simultaneously or continuously the drawing and the false twisting of the yarn to carry out the false twisting at high speeds. However, problems reside in the provision of a device capable of precisely carrying out the stable false twisting under high speeds and in the control of such a device to maintain operational stability during the false twisting process.
In order to remove such problems, until this time, the false twisting has been carried out by running the yarn while maintaining it in contact with either one of the outer peripheral surfaces of rotary discs or the inner or side surface of a cylinder, and the control for stable performance of the false twisting process has also been made by contacting discs which are rotated by a very small amount of torque to the running yarn under false twisting process and by detecting the number of twists of the yarn by calculation of the number of rotations of the discs. With such a false twisting method, the number of twists of the yarn is determined by the contact force of the yarn acting on the twisting surface of the rotary disc. Since this contact force depends on the tension of the yarn, considerably strong tension is required to obtain a large twisting force, and particularly, the untwisting side will require a tension larger than that on the twisting side, because on the untwisting side the yarn is drawn out. The application of the strong tension to the yarn makes it difficult to take up the yarn at high speed and this affects the quality of the twisted yarn.
To avoid the application of such strong tension to the yarn there has been proposed a method in which a yarn is inserted between the opposing end faces of two cup-shaped discs, and twisting and feeding forces are applied to the yarn by rotating the discs in the opposite directions. However, with false twisting apparatus of this prior type, an elastic material with high friction property, such as rubber, is applied to the yarn contacting surfaces of the rotary discs, which are adjusted and secured to a predetermined portion so as to provide a small gap between the facing yarn contacting surfaces of the discs or to cause the contact surfaces to contact each other with a suitable amount of contact pressure. Thus, the stable twisting force is applied to the yarn generally possessing a non-uniform diameter by putting the yarn between the contacting surfaces made of an elastic material.
However, even with this type of apparatus, because of the thermal expansion caused by the friction between the yarn and the elastic material on the discs and of the thermal expansion of the bearings utilized to support the rotary discs, it is difficult to clamp a fine yarn between the contacting surfaces of the opposing discs with a constant contact pressure, and in a case where liquid is required for cooling and lublicating the yarn contacting surface, the contacting portions, made of rubber, of the discs may become swollen by the liquid. For this reason, the gap between the contacting portions, which has been set by proper adjustment, may be narrowed or the contact pressure between the contacting portions may unnecessarily be increased. These defects have an effect on the quality of the twisted yarn, damage the contacting surfaces of the discs and in the worst case render the false twisting process impossible.
Furthermore, although the problem concerning the swelling of the contacting portions may be eliminated by using metal or material coated with ceramics or diamond as the contacting portions in place of the elastic material so as to keep a constant gap, such metal or material possesses no elasticity, so that it is difficult to clamp therebetween stably and firmly the yarn possessing a non-uniform diameter which varies depending upon the number of twists. It will also be impossible to remove adverse influences caused by the thermal expansion even if such metal or material is used.